Enhancement of oxidative stability of polyfluorenes for direct thermal lithography

A homopolymer of 9,9'-bis[4-(2-(2-tetrahydropyranyloxy)ethoxy)phenyl]fluorene and its copolymers with 3,4-benzothiadiazole and 4,7-di(3(4-n-octylphenyl)-2-thienyl)-2,1,3-benzothiadiazole were synthesized to produce a series of thermally reactive blue, green, and red luminescent polymers. Thermolytic removal of the tetrahydropyran (THP) group from polymer films, rendered the films insoluble due to the formation of hydroxyl groups on the termini of side chains. Thermal removal of the THP was lowered by up to 200 °C, when acid is present in the films. These polymers were found applicable to patterning by NIR direct thermal lithography, in conjunction with a NIR dye and thermal acid generator. The presence of the phenyl groups at the 9-site carbon was found necessary to eliminate fluorenone formation, and enhance the colour purity of the material.